22c Treat most subjects joined with and as plural.

A subject with two or more parts is said to be compound. If the parts are connected with and, the subject is nearly always plural.

The example reads,

Bleach and ammonia create (strikethrough) s (end strikethrough) a toxic gas when mixed.

EXCEPTIONS: When the parts of the subject form a single unit or when they refer to the same person or thing, treat the subject as singular: Fish and chips is always on the menu. When a compound subject is preceded by each or every, treat it as singular: Each tree, shrub, and vine needs to be sprayed.